North Liberty is a city in Johnson County, Iowa, United States. It is a suburb of Iowa City and part of the Iowa City Metropolitan Statistical Area. As of the 2010 census, the city population was 13,374. A special census taken by the city in 2004 counted 7,224 residents, while the Census Bureau's estimated 2007 population for North Liberty was 10,982.. From 2000 to 2010, North Liberty was the second-fastest growing town in Iowa.